The present invention relates to a radio wave receiving apparatus, which is provided with an antenna and a tuning circuit.
A communication apparatus is disclosed by Japanese Patent No. 2000-231609 A and Japanese Patent No. Hei 11-312959 A, which apparatus has an antenna and a tuning circuit connected to the antenna, and automatically adjusts a frequency characteristic of the tuning circuit to bring a receiving frequency of the antenna tuned in to a frequency of a desired wave. The communication apparatus is required to perform a tuning process to adjust the tuning circuit while receiving a transmitted radio wave, or it is necessary to use a separate oscillator, which generates a signal having same frequency as the actual radio wave, for performing the tuning process to adjust the tuning circuit of the communication apparatus. In the tuning process, a user changes capacitance of the tuning circuit to obtain a detected signal of the maximum level, or adjusts the tuning circuit to obtain AGC signal of the maximum gain, while monitoring AGC signal and/or a signal level of the detected signal obtained in the receiving process.
Meanwhile, a receiving circuit of the super heterodyne system has a problem that an image frequency can prevent it from obtaining the correct tuning point, if no modification is made.
An object of the present invention is to provide a radio wave receiving apparatus, which can obtain a correct tuning point of a tuning circuit that meets with a frequency of a desired wave, even if the tuning circuit is of the super heterodyne system.